The present invention relates to a pulse amplitude discriminating circuit. More specifically the invention relates to a discriminating circuit which remembers a pulse while a determination of the pulse height is made and then, if the pulse height falls within predetermined upper and lower levels the discriminating circuit, passes the pulse height of the remembered pulse to a pulse analyzing circuit.
Heretofore, various discriminating circuits have been proposed for use in particle analyzing devices for determining whether or not a particle pulse amplitude falls between upper and lower amplitude levels and for producing an output pulse if the particle pulse amplitude falls between the predetermined upper and lower levels. However, the previously proposed pulse discriminating circuits do not provide a memory means for remembering the pulse while a determination of pulse height is being made and for thereafter passing the pulse height to a pulse analyzing circuit. Examples of the previously proposed pulse amplitude discriminating circuits may be found in the following patents:
U.s. patent numbers PA1 3,127,505 PA1 3,259,842 PA1 3,271,671 PA1 3,331,950 PA1 3,392,331.
The discriminating circuit of the invention to be described in detail hereinafter, enables a technician to analyze the pulse heights of particles falling within predetermined upper and lower pulse height or amplitude levels and provides the technician with the pulse height of each pulse falling within the predetermined levels instead of merely providing pulses indicative of pulses falling within the predetermined levels. Such a circuit is especially useful in the measuring of the average volume of blood platelets which are the small particles in blood which are important in clotting. These platelets lie in the size range of approximately 3.5 to 35 cubic microns and are distinguishable from red cells by their small size. When making a platelet count, typically an attempt is made to separate the platelets from the red cells by centrifugation. However, this procedure is now wholly effective and is made doubly difficult by the fact that there are roughly 100 red cells for every platelet. Thus, a suspension of platelets is quite likely to have red cells in it. Accordingly, a pulse discriminating circuit of the type disclosed herein enables a technician to ignore pulses above a certain level such as those produced by red cells, while permitting the platelets to be counted and more particularly permitting a measurement of the average volume of blood platelets.
According to the invention there is provided in a system where particles in a fluid are caused to flow through a sensing zone and a particle pulse is generated for each particle sensed with the amplitude of each pulse being related to the size of the particle sensed, a pulse amplitude discriminating circuit for determining which pulses have an amplitude falling between predetermined upper and lower levels for remembering each pulse while the determination is being made and for passing to a pulse analyzing circuit only the pulse heights of those remembered pulses which have an amplitude falling between the predetermined upper and lower amplitude levels.
Also, according to the invention there is provided in a method for analyzing particles in a fluid by causing the particles to flow through a sensing zone where a particle pulse is generated for each particle sensed and the amplitude of each particle pulse is related to the size of the particle sensed, the steps of determining which pulses have an amplitude falling between predetermined upper and lower amplitude levels, remembering each pulse while said determination is being made, and passing to a pulse analyzing circuit only the pulse heights of those remembered pulses which have an amplitude falling between the predetermined upper and lower amplitude levels.